Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels.
Particulate matter sensors may encounter problems with non-uniform deposition of soot on the sensor due to a bias in flow distribution across the surface of the sensor. Further, particulate matter sensors may be prone to contamination from an impingement of water droplets and/or larger particulates present in the exhaust gases. This contamination may lead to errors in sensor output. Furthermore, sensor regeneration may be inadequate when a substantial quantity of exhaust gases stream across the particulate matter sensor.
The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a system for sensing particulate matter in an exhaust passage of an engine is provided. The system comprises a first outer tube with a plurality of intake apertures on an upstream surface, a second inner tube with a plurality of intake apertures on a downstream surface, and a particulate matter sensor placed within the second inner tube.
For example, a particulate matter (PM) sensor may be disposed within a second inner tube, the second inner tube being enclosed within a first outer tube. The first outer tube may have a plurality of perforations on an upstream surface of the first outer tube facing an oncoming exhaust flow. Further, the second inner tube may have a group of perforations distributed on a downstream surface of the second inner tube, the downstream surface facing away from exhaust flow. The PM sensor may include an electrical circuit on one of its surfaces, and the PM sensor may be positioned within the inner tube such that the surface with the electric circuit faces the intake perforations on the downstream surface of the second inner tube. Accordingly, a sample of exhaust gases may enter the first outer tube via the upstream perforations, flow around an annular space between the second inner tube and the first outer tube, and enter the second inner tube via the group of perforations on the downstream surface of the inner tube. The sample of exhaust gases may then impinge on and flow across the surface of the PM sensor with the electrical circuit. Finally, the sample of exhaust gases may exit the second inner tube via channels that fluidically connect the second inner tube with the exhaust passage.
In this way, a PM sensor may be exposed to a more uniform flow distribution across its surface. By guiding the sample of exhaust gases through two sets of apertures, the flow rate of the sample of exhaust gases may be controlled. Further, the flow rate may be more even as it impinges on the surface of the PM sensor allowing for a more uniform deposition of particulates. By providing a more even and controlled flow rate of the sample of exhaust gases onto the PM sensor surface, sensor regeneration may occur with reduced heat loss. Further, as the sample of exhaust gases is streamed through the annular space between the two protective tubes, larger particulates and/or water droplets may be deposited on the inner downstream surface of the first outer tube due to their larger momentum. Therefore, the PM sensor may be protected from impingement of water droplets and larger particulates. Overall, the functioning of the PM sensor may be improved and may be more reliable.
In another example, a PM sensor may be disposed within a single protection tube having a plurality of perforations on a downstream surface facing away from oncoming exhaust flow. Further, the protective tube may have one or more exit apertures positioned on side surfaces of the protective tube, where the side surfaces are tangential to the oncoming exhaust flow. Flowing exhaust gas around the protective tube, may create areas of lower pressure exterior to the side surfaces of the protective tube, relative to areas exterior to the downstream surface of the protective tube. Due to the pressure differential between the downstream and side surfaces of the protective tube, exhaust gas may naturally be drawn into the downstream perforations, onto the PM sensor, and then out of the protective tube through the exit channels on the side surfaces of the protective tube. Thus, the flow direction of a portion of exhaust gas flowing past the protective tube may be reversed, such that the portion of exhaust gas may flow towards the perforations on the downstream surface of the protective after having flowed past the protective tube.
In this way, a PM sensor may be exposed to a more uniform flow distribution across its surface. By guiding the sample of exhaust gases around the protective tube before entering the protective tube through the intake perforations on the downstream surface of the protective tube, the flow rate of the sample of exhaust gases may be controlled. Further, the flow rate may be more even as it impinges on the surface of the PM sensor allowing for a more uniform deposition of particulates. By providing a more even and controlled flow rate of the sample of exhaust gases onto the PM sensor surface, sensor regeneration may occur with reduced heat loss. Further, as the sample of exhaust gases is streamed from the downstream surface of the protective tube, the amount of larger particulates and/or water droplets impinging on the PM sensor may be reduced. Specifically, due to their larger momentum, water droplets and/or larger particulates may flow past the protective tube without redirecting their flow direction to enter the protective tube through the perforation on the downstream surface of the protective tube. Therefore, the PM sensor may be protected from impingement of water droplets and larger particulates. Overall, the functioning of the PM sensor may be improved and may be more reliable.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.